1. Field of the Invention
The present invention generally relates to a semiconductor device, and an apparatus and a method for manufacturing the same. More particularly, the present invention relates to a semiconductor device including a metal film formed on a semiconductor substrate in a specific region, and an apparatus and a method suitable for manufacturing the semiconductor device.
2. Description of the Background Art
FIG. 26 shows a flow chart of a sequence of processes performed in a former manufacturing method of a semiconductor device. The sequence of processes shown in FIG. 26 are performed for forming a metal film on a semiconductor substrate in a specific region including the interior of a contact hole, via hole, trench or the like (which is hereinafter referred to generally as "hole") provided in the semiconductor substrate. As shown in FIG. 26, the process of forming a metal film begins with a step 10.
At the step 10 is performed a degassing process in which a gas contained in a semiconductor substrate is released by heating the substrate to a specific degassing temperature in a vacuum atmosphere. The purpose of the degassing process is to prevent the formation of a metal film from being obstructed by the gas contained in the semiconductor substrate. Following the degassing process, a treatment at a step 12 is performed as needed.
At the step 12 is performed a sputter etching for enlarging a hole top, that is, a portion near an opening edge of a hole. The increased diameter of the hole top by sputter etching at the step 12 allows easy formation of a metal film in the hole. It should be noted that the sputter etching at the step 12 may be omitted.
The process goes on to a step 14 at which is performed a treatment of forming a metal film on the surface of the semiconductor substrate in a state that the substrate is heated to a specific film formation temperature.
At the final step 16 is performed a process of cooling the semiconductor substrate remaining heated at the film formation temperature to room temperature. In this way, one metal film is formed on the semiconductor substrate. Hereinafter, the above sequence of processes are referred to as "a first prior art process".
FIG. 27 shows a flow chart of a sequence of processes, different from those shown in FIG. 26, carried out in another former process for manufacturing a semiconductor device. The sequence of processes shown in FIG. 27 are performed for forming a stacked metal film composed of a plurality of metal films different in material on the surface of a semiconductor substrate. It should be noted that steps in FIG. 27 for performing the same processes as those at the steps in FIG. 26 are denoted by the same reference numerals, and the explanation thereof is omitted.
As shown in FIG. 27, in the process of forming a stacked metal film, after completion of a treatment of forming a first metal film (treatment at the same step 14 as that shown in FIG. 26), a treatment of forming a second metal film (treatment at a step 18) is performed.
At the step 18 is performed the treatment of forming the second metal film on the first metal film already formed on the surface of the semiconductor substrate, in a state in which the substrate is heated to a specific film formation temperature. Following this treatment, a treatment of cooling the semiconductor substrate to room temperature (at the same step 16 as that shown in FIG. 26) is executed, to thus complete the process of forming the stacked metal film. Hereinafter, the above sequence of processes are referred to as "a second prior art process".
In the first or second prior art process, during degassing or sputter etching is heated the semiconductor substrate to a temperature higher than the temperature required for formation of the metal film. Also in the second prior art process, the treatment of forming the first metal film may cause the semiconductor substrate to be heated to a temperature higher than the temperature required for formation of the second metal film. In particular, if the first or second prior art process is carried out using a fabrication apparatus capable of continuously performing the degassing process and the metal film forming process, there may arise a state in which the formation of a metal film begins under such a condition that the temperature of the semiconductor substrate is significantly higher than a required film formation temperature.
The coverage of the metal film in the hole, that is, the covering state of a metal film in a hole formed in a semiconductor substrate becomes worse as the temperature becomes higher of the substrate at the beginning of the formation of the metal film. The tendency of deteriorating the coverage of the metal film becomes significantly larger as the process temperature during the formation of the metal film becomes higher. For this reason, according to the first prior art process, it is not necessarily easy to obtain a good coverage of a metal film in a hole.
In the case of forming a stacked metal film composed of a plurality of metal films different in material, if the formation of a metal film on the underlying metal film thereof begins in a state that a semiconductor substrate is kept at a high temperature, the upper metal film may react with the lower metal film to form reaction products at the boundary between the lower and upper metal films. To ensure the accuracy of photolithography for a stacked metal film, a relatively thin reflection preventive layer having a low reflectance may be formed on the uppermost layer of the stacked metal film. In this case, if reaction products are formed at the boundary between such a reflection preventive layer and the underlying metal film, there may occur groove-like depressions due to the presence of the reaction products in the surface of the reflection preventive layer, that is, in the surface of the stacked metal film.
A stacked metal film is used as a base of metal wiring for a semiconductor device. After completion of the formation of the stacked metal film, the stacked metal film is thus subjected to etching for formation of the metal wiring. If a stacked metal film has groove-like depressions in the surface, foreign matters caused during etching for formation of metal wiring are easy to remain in the depressions, particularly, at sharp corners of end portions of the depressions. The remaining foreign matters will cause an etching failure, leading to short-circuit of a pattern of the metal wiring.
If reaction products formed at the interface between a metal film and the underlying metal film thereof have a high resistivity, the resistance of the metal wiring may increase by the presence of the reaction products. As a result, in formation of a stacked metal film, it is important to prevent formation of reaction products at the boundary between metal films different in material, particularly, between the uppermost metal film and the underlying metal film. According to the second prior art process, however, in formation of a metal film on the underlying metal film, the formation of the upper metal film begins in a state that the semiconductor substrate remains sufficiently heated. That is to say, according to the second prior art process, it is not necessarily easy to form a stacked metal film without formation of reaction products between metal films.